which of the indicated protons in this compound would have the smallest pka valu
ID: 1069335 • Letter: W
Question
which of the indicated protons in this compound would have the smallest pka value?
The answer for this problem is D, but I'm not sure why. The smallest pka proton should be the most acidic, AKA the one that produces the most stable carbanion after deprotonation. It seems to me like B, the position that can both resonate w/ the benzene ring and adjacent double bond would be much stabler than D. Additionally, I thought vinylic carbanions were unstable?
8. Which of the indicated protons in this compound would have the smallest pKa value? CH2-CH-CH-C C-H (A) A (B) B (C) C (D) DExplanation / Answer
The pKa of proton D is the smallest. This is because it is attached to an sp carbon (alkyne carbon). An sp carbon has largest s character compared to the sp2 and sp3 carbons, due to which its carbanion is the most stabilized. An alternate explanation is that due to largest s charater the alkyne carbon pulls bonding electrons towards itself and making C-H bond most acidic.
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